This week, President Obama is engaged in two challenges - possible U.S. military action against Syria and how to mark the 50th anniversary of the March on Washington, an iconic moment in the civil rights movement. Joining us now to talk about the president's week is NPR's national political correspondent Mara Liasson. And, Mara, talk about a military response from the U.S., and its allies seems to be getting stronger every day.

MARA LIASSON, BYLINE: Yes. The drumbeat is getting louder every day. The president is discussing military options with his advisers. He's consulting with allies around the world. He's talking to the relevant congressional leaders. And we now hear that U.S. intelligence officials are getting ready to release some intercepted communications that they believe will be even more evidence that it was Syrian President Bashar al-Assad who ordered this chemical attack.

You know, the president has done everything he can to avoid another foreign military involvement, but he can't avoid it after the widespread use of chemical weapons on this scale. So if the Syrian regime has been testing the U.S. limits, they appear to have found them.

BLOCK: And, Mara, there a lot of questions about what the purpose or goal would be of any potential strikes in Syria.

LIASSON: Well, that's a very good question, and there's a big debate about this. The question is: Is the purpose to send a proportionate message just as a punishment or - as others have been urging - to do something that will help change about the power on the ground, to try to degrade Assad's forces, to try to tilt the military dynamic away from Assad who, along with his allies Iran and Hezbollah, has been winning the conflict so far, or is it merely to send a message that the use of chemical weapons will have consequences however minimal and symbolic? This is what the White House Press Secretary Jay Carney said today.

JAY CARNEY: To allow it to happen without a response would be to give a green light to the Assad regime, and other potential users of chemical weapons, that there will be no consequences.

LIASSON: Other potential users means Iran. It's - this is not just about chemical weapons. It's not just about Assad. This is a proxy war. Iran, who is developing its own weapons of mass destruction, is currently backing the Syrian regime, and it is watching very carefully to see what the U.S. does. So the decision that President Obama is making now will have consequences for the whole region. The question is after the U.S. cruise missiles strikes are over, will Syria and Iran feel emboldened or chastened? What happens afterwards? Will the region see it as a symbolic strike or whether it actually had a strategic effect?

BLOCK: Mara, Jay Carney also did have language today about whether this - the goal of the strikes would be regime change. What did he say?

LIASSON: Well, he absolutely ruled that out. He said that is not the purpose. But there a lot of strategic goal short of regime change that the U.S. could try to reach. The problem is that the president has been trying very hard not to get involved, not to get on another slippery slope to deeper military involvement in the Middle East. But what if a limited surgical strike doesn't have the desired effect? He could be on that slippery slope whether he wants to or not.

BLOCK: Well, Mara, the talk about military action in Syria has overshadowed the other big event this week, and that's the 50th anniversary of the March on Washington. President Obama will be speaking tomorrow on the steps of the Lincoln Memorial.

LIASSON: That's right. It's a big anniversary, a very big speech. The president will not try to compete with the famous "I Have a Dream" speech by Martin Luther King, but he will mark it. There is one bit of suspense about the speech, which is to what extent, how much attention, will President Obama give in that speech to the voting rights cases that his Justice Department is currently bringing?